1. Field of the Invention
The present invention relates to a charged-particle beam system (i.e., an analytical instrument using an electron beam or ion beam) equipped with a cryogenic specimen stage and adapted for imaging and analyzing a specimen and, more particularly, to a specimen stage-moving device enabling Z motion of such a specimen stage.
2. Description of Related Art
Generally, where a medical or biological specimen is observed with a charged-particle beam system, if the specimen is irradiated with an electron beam, the morphology may be destroyed. As a result, it may not be possible to observe the specimen under normal state. In this case, if the specimen is cooled cryogenically, the specimen is less likely to be destroyed by electron beam irradiation and it is possible to observe the specimen under normal state. A known specimen-cooling device is described in Japanese Patent Document JP-A-2000-208083 cited below. This specimen-cooling device has a specimen-holding member, two refrigerant tanks for storing two kinds of refrigerants for cooling a specimen, and two capillaries for placing the tanks in communication with a refrigerant reservoir. The specimen-holding member is centrally provided with a specimen-holding portion for holding the specimen. The refrigerant reservoir is formed in an outer portion of the specimen-holding portion and holds the refrigerants therein. The specimen-cooling device has a mechanism for selectively supplying the two kinds of refrigerants to the refrigerant reservoir.
Known cryogenic specimen-tilting devices permitting a specimen to be imaged and analyzed while the specimen is cooled and tilted are described in the Japanese Patent Documents JP-A-2002-134053 and JP-A-2007-26815. JP-A-2002-134053 discloses a tilting device permitting a specimen to be imaged while the tilt angle of the specimen is being adjusted under the condition where the specimen is cooled down to a low temperature. JP-A-2007-26815 discloses a rotary member for tilting a specimen stage. The rotary member can adjust the specimen to a large tilt angle while the specimen is cooled cryogenically. Furthermore, the rotary member can make the specimen holder smaller and thinner.
In a charged-particle beam system equipped with a cryogenic top-entry specimen stage, a specimen can be imaged and analyzed while the specimen is cooled and moved or tilted in the X- and Y-directions by the prior art.
However, this system is not equipped with any Z-motion mechanism. If a Z-motion mechanism can be equipped in the prior-art charged-particle beam system having a cryogenic top-entry specimen stage, then tomography will be enabled. The tomography is a technique of reconstructing a three-dimensional internal structure of a specimen by tilting the specimen continuously, taking multiple projection images, and image-processing the images by a computer.